What is the difference between “0” and “?” under Page views in a Page table?

If you subscribe to Analytics (or Traffic) and the Content suite then page tables normally show page views for the previous 30 days.

In some cases, the number of page views is not shown but instead a “0” or a “?” is displayed.

• “0” indicates that the page has previously had page views, but no page views have been seen in the last 30 days.
• “?” indicated that Siteimprove has never registered a page view for this URL.
  This can be due to a mismatch between the URLs found by our crawler and those registered by Analytics/Traffic. Please contact Siteimprove technical support if you would like us to investigate further in this case.

Screenshot of a page table in the content suite